(i) Field of the Invention
This invention relates generally to an improved process for preparing alkyldiarylphosphines and related compounds. The related compounds include those wherein the phosphorus atom is replaced by any other trivalent atom from Group VA of the Periodic Table. More particularly, the invention relates to a first step of a process in which a first halide (such as diphenylphosphinous chloride) is reacted in solution with an excess of an alkali metal (such as molten sodium). The second step of the process concerns reacting the reaction product of the first stage with a second halide (such as chlorohexane) thereby forming hexyldiphenylphosphine which is thereafter separated. The improvement features particularly relate to greater yield, use of critical amounts of alkali metal, and a single reactor rather than two reactors. Novel products prepared by the process include behenyldiphenylphosphine.
(ii) Description of the Prior Art
A computer search of Chemical Abstracts over the period 1967 to present, turned up only three references directed to n-hexyldiphenylphosphine and having the corresponding CA code number "RN-18298-00-5". None of these references relate to processes for preparing phosphines (or related products such as arsines), but rather to their properties and utility, as summarized below.
U.S. Pat. No. 3,322,542 (Ullmann et al) is entitled "Stabilization Additives for Photochromic Compounds". Its Example 49 relates to the use of "diphenylhexylphosphine" (DPHP) as such an additive, and a number of the other examples relate to the use of other phosphines.
"Allylic Alkylations Catalyzed by Nickel" by Cuvigny et al. in J. Organomet. Chem., 250(1), C21-C24, apparently also refers to the use of hexyldiphenylphosphine as a catalyst for allylic alkylation of enolates.
"Carbon-13 NMR Spectra of Tertiary Phosphines, Arsines, and their Onium Salts" by Koketsu in "Physical Organic Chemistry", Vol. 12, at pages 1836-43 reports the 13C-NMR spectra for compounds containing a phosphorus or arsenic atom, including alkyldiphenylphosphines such as hexyldiphenylphosphine.
"The Preparation and Reactions of Diphenylphosphinous Chloride" by C. Stuebe et al. in J. of the Amer. Chem. Soc., Vol. 77, pgs. 3526-3529 (1955) includes a method of preparing hexyldiphenylphosphine at pgs. 3527-3528. It points out that diphenylphosphinous chloride reacts readily with Grignard reagents to give tertiary phosphines in good yield. From FIG. 1, a "good yield" appears to be 70-75%. It is believed that this reaction would not be easy to run on a plant scale.
"The Free Radical Addition of Phosphines to Unsaturated Compounds" by M. M. Rauhut in The Journal of Organic Chemistry, Vol. 26, pages 5138-5143 (1961) describes the preparation of octyldiphenylphosphine by the free radical initiated addition of diphenylphosphine to 1-octene, and other related compounds. This reaction is generally low yielding and difficult to carry to completion.
In addition to the foregoing, three references are known which disclose 2-step processes having some similarities to the invention claimed hereinafter. They are discussed below.
"Diphenyl(trimethylsilyl)phosphine and Dimethyl(trimethylsilyl)phosphine" by R. Goldsberg and K. Cohn in Organic Syntheses Volume XIII, published by McGraw-Hill, (1972), at pages 26-29 states that diphenyl(trimethylsilyl)phosphine has been prepared in yields above 60% by the reaction of chlorotrimethylsilane with sodium diphenylphosphide in constantly refluxing n-butyl ether. The sodium diphenylphosphide is prepared from commercially available diphenylphosphinous chloride. Although the initially formed product is the tetraphenyldiphosphine, the phosphorus-phosphorus bond is cleaved by the action of excess sodium to give the sodium salt. The stated reactions are shown below. ##STR1##
The working Example described at pages 27 and 28 used about 120% excess sodium in the first step of the process (since 0.65 mole of sodium was used in conjunction with 0.15 mole of diphenylphosphinous chloride, rather than the 0.30 mole of sodium theoretically needed for the reaction). Further, the suspension of sodium diphenylphosphide was transferred to a separate vessel prior to the commencement of the final reaction and the excess sodium remained behind in the original vessel.
"Diverse Donor Properties exhibited by the Facultative Diphosphine Diether Ligand, 1,8-Bis(diphenylphosphino)-3,6-dioxaoctane: Six- and Four-coordinate Complexes and trans Bidentate Behaviour" by William E. Hill et al. in J. Chem. Soc. Dalton Trans. (1982) at pages 833-839 also discloses a first-step process including the preparation of sodium diphenylphosphide slurry. The working example (at the bottom of page 837 and the top of page 838) indicates that 0.65 mole of sodium metal was used in conjunction with 0.10 mole of diphenylphosphinous chloride. Further, the diphenylphosphide slurry was transferred to a separate vessel and implicitly the excess sodium remained in the original vessel prior to the next step of the process.
U.S. Pat. No. 4,166,824 (Henderson) relates to a chiral biphosphine-rhodium complex as a catalyst for the asymmetric reduction of a tetramisole precursor which allows the synthesis of levamisole in high optical yield. Example 5 is hereby incorporated by reference. It includes a description of the preparation of an intermediate product mixture containing sodium diphenylphosphide and unreacted sodium. The "ditosylate product of Example 4" was added to the foregoing intermediate product in situ. However, it appears that (1) the percent yield of the final product (i.e., "Formula 1 in Sequence 1") was extremely low; (2) the unreacted sodium corresponded to at least 100 percent excess; (3) the "ditosylate product of Example 4" is not a halide; and (4) the particle size of the sodium is not indicated.
Essentially, nowhere does the prior art disclose or suggest the type of process claimed hereinafter wherein the amount of excess sodium is less than 100% or wherein the conversion efficiency is greater than 70%.